The present invention relates to coatings and more particularly to a process for preparing color-developer materials useful as coatings in pressure-sensitive copy systems.
One type of pressure-sensitive copy paper produces a distinctive color in a region of localized pressure as a result of an acid-base reaction in the region. Generally, an electron-donating or basic, colorless, chromogenic compound reacts with an electron accepting or acidic material in the region through the medium of a oily, water-immiscible solvent.
This type of pressure-sensitive copy paper may consist of a transferring paper coated with a layer of microcapsules, containing an electron-donating, colorless chromogenic compound dissolved in an oily solvent, and juxtaposed receiving paper coated with a layer of an electron-accepting material and a suitable binder. When localized pressure is applied, e.g., by handwriting or typewriting, the microcapsules rupture in the region under pressure. The colorless chromogenic compound released from the ruptured microcapsules is transferred to the receiving paper and reacts with the electron-accepting material to form a definite colored mark.
A variant form of such pressure-sensitive copy paper consists of a sheet on which microcapsules containing a chromogenic compound dissolved in an oil are intermixed with microcapsules containing an electron-accepting material. Examples of such pressure-sensitive copy papers and microcapsules are described in U.S. Pat. Nos., 2,712,507; 2,730,456; 2,730,457 and 2,800,457.
Another variant form of such pressure-sensitive copy paper consists of a sheet on which microcapsules containing a chromogenic compound dissolved in an oil are coated on a substrate and dried, followed by a second coating containing an electron-accepting material. An example of such a pressure-sensitive copy paper is described in U.S. Pat. 3,906,123. Pressure-sensitive copy papers comprising colorless, chromogenic compounds and acidic receptor materials on the same surface are known as "self-contained" systems.
When organic acid compounds or metal salts of organic acid compounds have been used as an acidic receptor in coatings for pressure-sensitive copy systems they generally are provided in a finely dispersed form, either by grinding the organic material together with an extender or by precipitating it in the presence of an extender. It is important that the organic acid receptor material be extended with an inert or adsorbent particulate filler, usually an inorganic filler such as clay or alumina, to make the most efficient use of the relatively costly organic material and to present a large surface area for reaction with the oily solution of basic chromogenic comound to facilitate rapid color development. In one instance, the organic acidic material has been extended by dissolving it in finely divided organic polymeric particles, in contrast to the inorganic extenders commonly used.
A process for making an activated, clay-coated paper for use as a pressure-sensitive copy paper is described in U.S. Pat. No. 3,928,702. Acidic activated clay is mixed with a water-dispersible emulsion of a hydrophobic oily material. This patent is concerned with making the non-chromogenic acid in the clay more accessible to colorless, electron-accepting, chromogenic material contained either in microcapsules or on an independent layer.
It is an object of this invention to provide a uniform distribution of acid organic acceptor material on an inert or reactive adsorptive, particulate extender. It is a further object of this invention to provide a means for dispersing and extending soft, amorphous, oily or tacky organic acid acceptor materials which would be incompatible or more difficult to process with a grinding or precipitation method of dispersion.
In addition to pressure-sensitive copy systems, the resulting emulsions or dispersions also are useful in coatings for heat-sensitive and stencil copy systems using colorless, chromogenic compounds.